Usually, it's because the sperm gets into the fallopian tube before the egg is released. Once there, the sperm wait for an egg to arrive. After fertilization, it can take 5-10 days for the fertilized egg to begin to attach itself to the lining of the uterus. Pregnancy begins when this happens.
The arrangement of spikes originally had no distinct name; the term Thagomizer was coined in 1982 by cartoonist Gary Larson in his comic The Far Side, and thereafter became gradually adopted as an informal term within scientific circles, research, and education.
Stegosaurus had a formidable tail. Studded with four long spikes, this dinosaur's business end would have given Allosaurus and other Jurassic predators plenty of incentive to keep moving. But do we have any evidence that Stegosaurus really used its tail this way? Among paleontologists, the four-spiked tail of Stegosaurus is called a  thagomizer.. It is one of a few terms inspired by one of Gary Larson's beloved  Far Side cartoons: a caveman points to a slide of a Stegosaurus tail and names the nasty-looking structure in honor of the late Thag Simmons..